High-speed steel



Patented Jan. 2, 1940 UNITED STATES PATENT OFFICE Firth, Pittsburgh,

Pennsylvania Pa., Sterling Steel Company,

assignors to Firtha corporation of No Drawing. Application November 18,1938;"

Serial No. 241,228

ZCIaims.

In the manufacture of high-speed steels it long has been known thattungsten may be replaced wholly or in part by molybdenum, and suchreplacement has been recognized to be in a general way valuable,affording tools of superior durability. See Gregg, The Alloys of Ironand Molybdenum, published for the Engineering Foundation, New York andLondon, 1932, p. 315. It has, however, been additionally found that, inthe heat treatment of tools made from molybdenum steel, a softening willoccur of the metal on and near the surface; and the softening has beenfound to 'be due to the burning out of the molybdenum. And it has beendeemed advantageous to include in the mix a substantial chromiumcontent, in order to counteract this bad tendency.

We have discovered that, given certain limiting conditions, molybdenummay be the chief and practically the whole substituent for the tungstenof the typical high-speed steel, and chromium may be substantiallyeliminated. This with the advantage that in the tool produced from thesteel greater red-hardness is gained, greater cutting efilciency, andgreater length of service. The limiting condition is the presence ofboron. If, in a tool steel of otherwise normal mix, in which the carboncontent does not exceed 1.00 per cent of the iron, boron be present inan amount ranging fromone quarter to one half of the carbon content, andif the chromium content be reduced to a quantity not exceeding 1.50 percent, or even eliminated entirely, it becomes possible to produce a toolsteelwhose molybdenum content ranges near to 8, say from '7 to 10 percent, and the tool produced from the steel will have the superioritythat has been indicated. The tool maybe treated in the usual mannerwithout loss of hardness in consequence of the escape of molybdenum andof carbon from the surface of the tool. The boron appears to cause athin film of molybdenum or iron-molybdenum borides on the surface whichinhibits the burning out of molybdenum and carbon. As has beenindicated, the carbon content should not exceed 1.00 per cent. It willpreferably range from .50 to 1.00 per cent.

In the practice of the invention the preparation of the melt is alongthe usual lines. The molybdenum is introduced in the form offerromolybdenum, and the boron as ferro-boron or boron carbide. Themetallurgist will understand how to proceed in detail. The metal iscastandforgcdlnregularprocedureandthe shaped article is subjected to thehardening and tempering steps that are familiar in the art.

Other alloying ingredients used in high-speed steels may be added fortheir usual efiects. For example, vanadium from .50 to 2.00 per centincreases toughness and raises the drawing temperature. Cobalt canbe'added up to 10 per cent. It raises the hardening and drawingtemperatures, increases the red-hardness, and toughens the steel. Copperup to 2 per cent helps in the forging and aids in the prevention ofdemolybdenizing or decarburizing. Nickel up to 5 per cent reduces thehardening temperature and reduces the hardness but does not affect thedrawing temperature. It tends to make the alloy tougher. Tungsten insmall amounts up to 2 per cent may replace part of the molybdenum butthis is not recommended.

This improved steel may contain:

Boron The following are analyses of the non-ferrous contents of seventypical steels of the invention, the quantities of the several contentsare given in percentages, relatively to the iron content:

I n IV v -VI VII 1.00 10:;; low low 'ifi .-75 1.25 1120 3:25 1:25

Of these, I, 11, and VI have been found to be most excellent.

Yet another steel was compounded upon the following analysis: carbon.75; silicon .25; manganese low; chromium .65; vanadium 1.25; molybdenum8.00; cobalt 8.00; boron'.40. This proved to be an excellent high-speedsteel. It will be observed of it that whilc the boron content slightlyexceeds, it is substantially one half 'of the carbon content. 7

We claim as our invention:

1. A molybdenum tool steel carrying as alloys 5 of the ferrous metal:

Per cent Molybdenum 8.10 Vanadium 1,36 Bor n .22

10 Chromium 1.07 Cobalt 2.59 Carbon .73

2. A molybdenum tool steel carrying as alloys of the ferrous metal ELMERB. WELCH. LEWIS GERALD FIR'I'H.

